This invention relates to a process of forming a multi-ply laminate which comprises at least one ply of glass and at least one ply of thermoplastics material forming an outer ply of the laminate, such process comprising assembling the plies of the laminate, degassing its inter-ply space or spaces and subjecting it to bonding conditions including environmental laminating pressure distributed over the outside of the or each said thermoplastics outer ply by a moulding plate.
Such laminates can be used for various purposes, but commercially the most important use probably lies in te field of glass/plastics laminates used as lights for motor vehicles, especially windscreens. Windscreens in which a said thermoplastics ply is exposed to the interior of the vehicle can have a combination of properties which is highly desirable for affording protection to vehicle occupants against laceration by glass fragments in the event of the windscreen being broken for example by impact of an occupant's head against the screen.
It will be apparent that such a product should be as optically perfect as is consistent with a commercially viable sales price.
Laminates of the form to which the invention relates are of potential value for other purposes, for example as interior or exterior glazings in buildings or other structures. The invention is also useful in the manufacture of opaque products, for example mirrors, especially those of the type in which a reflective layer is sandwiched between a glass sheet and a thermoplastics sheet of which one is tinted so as to afford different reflective properties according to the side from which the mirror is viewed.
Laminates of the said form include laminates having only two plies and also laminates having three or more plies. One or both outer plies may be of thermoplastics material. The laminate may include one, or more than one, glass ply, e.g. it may include a sub-laminate comprising two sheets of glass bonded together by means of a thermoplastics interlayer.
Plastics and glass plies of the laminate can be bonded by activating the thermoplastics with or without the use of an adhesion promoter or by means of an adhesive.
In order to avoid the entrapment of air between the plies of the laminate during its bonding, the assembled plies are subjected to a degassing step in order to remove any air from the inter-ply space. The entrapment of such air would lead to non-uniform bonding and would also be a cause of optical defects.
After degassing has commenced, the assembly is subjected to bonding conditions including heat and laminating pressure exerted on the outer main faces of the assembled plies.
It has been found that the manner in which such an assembly has hitherto been subjected to bonding conditions is a cause of non-parallelism of the outer faces of the laminate around the margin thereof thus leading to distortion of objects viewed through such margin. It is an object of the present invention to go at least some way towards remedying this defect.